With this app, that is compatible with cyanogenMod basedROMs,you can set the lockscreen wallpaper.
To set a specific wallpaper, just open your gallery app,selectthe image that you want to set as wallpaper then click thesharebutton and select this application.
If you want to automatically change the wallpaper usingtheimages in a folder, simply select the folder pathname andtheupdate interval.
In any case remember that for best results you must firstcropthe images to your smartphone screen size.